The production of foams based on polyols and isocyanates frequently utilizes cell- and foam-stabilizing additives to ensure a uniform and low-defect foam structure and hence to exert a substantially positive influence on the performance characteristics of the foamed material. Surfactants based on organically modified siloxanes are particularly effective and therefore represent a preferred type of foam stabilizer.
When these siloxanes are added in the course of the foaming process, the siloxanes are not only in pure form, but in the form of admixtures with further non-silicon-containing components. This can serve to improve meterability, since the amounts of siloxane to be added to the mixture to be foamed are often very small. In addition, the admixed component can also improve the solubility of siloxanes in the polyol mixture and hence additionally influence the foaming process and the foam properties.
It can be advantageous for the admixed component to also have surfactant properties that exert a positive influence on the foam properties. Recent demand has been for producing polyurethane foams that contain very small amounts of siloxane foam stabilizers, or even no siloxane foam stabilizers.
Various foam stabilizers and/or admixed components are known from the prior art:
EP 0839852 A2 describes the production of polyurethane foam using siloxanes in admixtures with vegetable oils consisting of different triglycerides. The oils however do not appear to have any influence on foam quality.
German Applications DE 1802500 and DE 1802503 describe alkanolamides obtained, for example, by reaction of diethanolamine with natural fatty acids or naturally occurring glycerides, and their use as a polyol component in the production of polyurethane foams. The description mentions the possibility that the use of siloxane surfactants can be dispensed with. In the aforementioned German Publications, the amides are used as the polyol component and thus constitute an appreciable part of the formulation. Foam production in the examples utilizes silicones as a stabilizing additive, which are used in fractions of below 5% based on the amide.
Similarly, German Applications DE 1745443 and DE 1745459, and U.S. Pat. No. 3,578,612 describe alkanolamides of polymeric fatty acid or alkoxylates thereof which are used as a polyol component for producing polyurethane foams. The foaming process always includes a siloxane stabilizer in small amounts (below 5% based on the amide).
EP 0767199 describes the use of soya-based diethanolamide for improving pentane solubility. Commercially available siloxanes are used as a stabilizer in the foaming process. The fractions of diethanolamide are at least 20 times higher than the fractions of siloxane. Hence the siloxane fraction is below 5% based on the amide.
U.S. Pat. No. 3,629,308 describes butanol-started polyethers useful as an admixed component for organosiloxanes.
EP 0048984 B1 describes admixtures of siloxanes with various water-soluble surfactants for use in a polyester-polyurethane foam. The surfactants mentioned in the aforementioned European publication are often poorly biodegradable.
EP 0043110 A1 describes admixtures of siloxanes with solvents such as, for example, alkoxylates onto glycerol, water, TMP, butanol or nonylphenol for use in a high-resilience polyurethane foam.
U.S. Pat. No. 5,236,961 describes the production of polyurethane foams using alkylphenol ethoxylates as foam stabilizers. The alkylphenol ethoxylates disclosed in the '961 patent originate from petrochemical sources.
EP 0734404 describes the production of polyurethane (PU) foams using polyalkylene oxides, wherein the polyalkylene oxides are constructed using 10-90% of butylene oxide.
Many of the foam stabilizers described in the prior art, more particularly those based on silicon, and/or their admixed components are notable for unfavorable toxicity, poor biodegradability or sensitivity to hydrolysis.
The use of polyurethane foams as insulation materials especially requires such polyurethane foams to have a small coefficient of thermal conductivity (lambda value).